The reduction in the discharge volume of carbon dioxide known as global warming gas is a theme on a global scale. While solar energy, wind power, geothermal energy and others have been developed, development and demonstration tests have been internationally advanced about a technique of separating and recovering carbon dioxide in a combustion exhaust gas discharged when fossil fuels such as coal are used, and then accumulating recovered carbon dioxide in the ground. In particular, about facilities from which a large volume of carbon dioxide is emitted, such as thermal power generation plants, it is necessary to develop a technique of separating and recovering carbon dioxide on a large scale.
In such facilities, such as thermal power generation plants, studies have been made about a technique of using an amine compound to absorb carbon dioxide selectively to separate and recover carbon dioxide in exhaust gas. In this recovery technique, a heat source is required when carbon dioxide is separated and recovered from the amine compound. For this heat source for carbon dioxide separation and recovery, the use of steam generated from boilers of thermal power generation plants has been so far studied (Patent Literature 2).
FIG. 6 schematically illustrates a power generation plant, and a conventional carbon dioxide separation and recovery apparatus installed together therewith. As illustrated in FIG. 6, in this plant, which is a power generation plant 1, steam generated by a boiler 3 is introduced into a steam turbine 4 to rotate a power generator 5, thus generating electric power. The steam that has been finished a work thereof in the steam turbine 4 is condensed in a condenser (steam condenser) 6, and then returned again to the boiler 3. In the meantime, a combustion exhaust gas from the boiler 3 is cooled, and then supplied to an absorption tower 7 of an apparatus 2, which is the carbon dioxide separation and recovery apparatus, from the downside thereof. In this tank, the gas is brought into contact with an aqueous solution of amines, such as monoethanolamine, which are carbon dioxide absorbents for recovering carbon dioxide, at, for example, 40° C. The combustion exhaust gas from which the recovery of carbon dioxide has been finished is sent from the top of the absorption tower 7 to a chimney 11, and then discharged into the atmosphere. The aqueous amine solution in which carbon dioxide has been absorbed is sent to a regeneration tank 8, and carbon dioxide is desorbed and recovered from the aqueous amine solution in this regeneration tank 8. The desorption and recovery of carbon dioxide is attained by heating the aqueous amine solution to 120° C. At this time, steam is used as a heat source which has a high temperature of 120° C. or higher and has been bled from the steam turbine 4 of the power generation plant 1, as represented by an arrow 12. The high-temperature steam, which has been bled from the steam turbine 4, is supplied to a heat exchanger 9. By effect of a heated medium generated by heat exchange therein, carbon dioxide is desorbed and recovered from the aqueous amine solution in the regeneration tank 8.
It is known that in the conventional carbon dioxide separation and recovery apparatus 2, a large calorie, such as a calorie of 2.5 to 4.0 GJ/ton of CO2, is required for the desorption of carbon dioxide (Nonpatent Literature 1). When steam having the calorie required for the desorption is bled from the steam turbine 4, a problem is caused that the power generation amount in the power generation plant 1 is decreased.
Outlet steam generated in the boiler 3 is inflated at the final stage of the steam turbine 4. Thereafter, the outlet steam turns low in temperature and pressure. The low-temperature and low-pressure steam still has thermal energy latently. However, the steam is returned to water in the condenser without attaining any work actually. Accordingly, if the low-temperature and low-pressure steam is taken outside the boiler system and then compressed to be raised in temperature, the steam can be effectively used. Actually, however, the steam emits latent heat thereof in the condenser 6 at the downstream to be returned to a liquid (water). Thus, it is desired to use the low-temperature and low-pressure steam effectively. In the conventional carbon dioxide separation and recovery apparatus 2 illustrated in FIG. 6, the aqueous amine solution is used as a medium for capturing carbon dioxide. However, the same problem is caused in a carbon dioxide separation apparatus using an adsorbent in which an amine compound is carried on solid particles (Patent Literature 1).